Oil and gas wells typically produce oil and gas along with byproducts, such as water. These byproducts can be resident in a formation, or can be introduced into a formation, for example, to assist in producing oil or gas from the well. For example, oil wells are often stimulated using enhanced recovery methods, such as water injection, steam injection, natural gas reinjection and gas lift, to increase rates for recovering oil from the wells. The water (or other fluids) introduced into the formation can flow into a well and mix with the oil. As a result, the well may produce a fluid mixture of water and oil. Tracking or otherwise determining the water content in oil, also referred to as “water-cut,” can be useful for many reasons. For example, water-cut measurements can be used during production to determine rates for introducing fluids in to a formation or well during the above described enhanced recovery methods, in feasibility analyses of oil wells, in monitoring refining processes (e.g., processes for desalting oil), for managing pipeline use, and so forth. Accordingly, many areas, including efficient oil production and refining processes, can benefit from economical systems and methods for obtaining precise measurements of water-cut.